/*
 * Copyright (c) 2005, Swedish Institute of Computer Science
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * This file is part of the Contiki operating system.
 *
 * @(#)$Id: random.c,v 1.2 2008/02/10 12:30:57 oliverschmidt Exp $
 */

/*
  From:
  
   D. Seetharam and S. Rhee, ``An Efficient Random Number Generator
   for Low-Power Sensor Networks'' First IEEE Workshop on Embedded
   Networked Sensors (EmNets-I), November 2004.
   
   http://www.dseetharam.org/papers/emnets.pdf
*/

#include "lib/random.h"
#include "sys/clock.h"

static clock_time_t time;

static unsigned short key;

void
random_init(unsigned short seed)
{
  key = seed;
}

unsigned short
random_rand(void)
{
  unsigned short rv, tv;

  rv = tv = 0;

  tv = (unsigned short)(time + clock_time());
  rv = tv ^ key;

  key = ~tv + 4711;
  tv = ~rv;
  time = tv;
  
  return rv;
}
